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Physics - X-Ray I > Electricity & Magnetism > Flashcards

Electricity & Magnetism Flashcards

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1
Q

Define Electricity

A

A form of energy associated with stationary or moving electrons or other charged particles

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2
Q

Electric charges exert …

A

forces on one another

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3
Q

Like charges…

A

repel

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4
Q

Opposite charges…

A

attract

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5
Q

The magnitude if the force between the charges depends upon…

A

the medium in which they lie and its maximum in a vacuum

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6
Q

The magnitude of force is inversely proportional to…

A

the distance between the charges, the smaller the distance, the greater the force

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7
Q

Coulomb’s Law

A

F is inversely proportional to q1xq2 / d2
F = force (newtons)
q1 and q2 = 2 charges (coulombs)
d = distance apart (metres)

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8
Q

Describe a photon and give an example

A

a small bundle of energy with no charge and no mass, x-rays and gamma rays are photons

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9
Q

Describe charge

A

measured in coulombs, a single charge can exist in isolation, 1 coulomb is the charge carried by 6.25 x 10 to the power 18 electrons

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10
Q

1 coulomb is …

A

the amount of charge that flows during 1 second if there is a current of 1 ampere

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11
Q

Define Field and give an example

A

A field is any region in space where a particular entity exerts its influence - e.g. electric, magnetic, gravitational
(Always remember fields are 3D)

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12
Q

The direction the lines point in an electric charge diagram show …

A

the direction in which an isolated POSITIVE charge would move if placed at any point in the field

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13
Q

The strength of a field is indicated by…

A

how close the lines are together

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14
Q

When an electric field is associated with 2 parallel plates, the direction of the electric field is …

A

postive to negative

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15
Q

A postive electrode is called …

A

anode

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16
Q

A negative electrode is called …

A

cathode

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17
Q

When does an electron move

A

when there is a difference in the electrical potential or ‘potential difference’ (p.d.)

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18
Q

What is the unit of p.d.

A

volts (V)

19
Q

Why can we measure energy in electronvolts (eV)

A

because an electron moves when placed in an electric field - as it moves it gains kinetic energy, the higher the voltage, the more kinetic energy it gains

20
Q

Describe the electronvolt (eV)

A

This is the amount of energy gained by an electron when it moves through a p.d. of 1 volt

21
Q

Describe an electric current

A

whenever a charged particle moves (A)

22
Q

Material through which a current flows is called a …

A

conductor

23
Q

Electric currents can flow through

A

solid, gases and vacuums

24
Q

To have a circuits there must be …

A

a potential difference and no gaps

25
Q

How are Voltage, Current and Resistance in a circuit related?

A

By Ohm’s Law

26
Q

Describe Ohm’s Law

A 
The current (I) flowing through a metallic conductor is proportional to the potential difference (V) across it, provided that all its physical conditions (e.g. its temperature) remains constant
I is proportional V
27
Q

Describe resistance

A

the opposition a material presents to a flow of electrons - measured in ohms

28
Q

Describe an insulator

A

a material whose electrical resistance is so high that current cannot normally flow through it (e.g. rubber, plastic, wood)

29
Q

The resistance of a conductor can be introduced to Ohm’s Law and rewritten …

A

I = V/R

30
Q

Definition of the Ohm

A

A conductor is said to have an electrical resistance of 1 ohm if a potential difference of 1 volt across it produces an electrical current of 1 ampere through it

31
Q

Transformers

A

increase or decrease voltage

32
Q

There are 2 types of magnetic pole …

A

north & south, like poles = repel, opposite poles = attract

33
Q

Main/Only difference between electricity and magnetism

A

A single magnetic pole cannot exist in isolation but a single charge can exist in isolation

34
Q

Magnetic Flux Density

A

the number of lines in a given area of space, measured in Tesla

35
Q

A magnetic field is only present when …

A

the current is on

36
Q

Formula to find the force between two magnetic poles

A

F is proportional to m1 x m2 / d2

37
Q

The lines of force are …

A

circular and concentric with the long axis of the wire

38
Q

The direction of the field depends on ..

A

the direction of the current

39
Q

Name the 3 factors affecting the strength of the magnetic field in a current-carrying solenoid

A

The number of turns - as number increases, the number of lines of magnetic flux increase in proportion
Current - as it increases through the coiled wire, the magnetic field strength increases up to a maximum
presence of ferromagnetic (soft iron) core - inserting a care through the centre of the wire greatly increases the magnetic field

40
Q

If a current is flowing through a resistance (e.g. wire) it causes …

A

heat to be generated and therefore wastes energy

41
Q

Most MRI systems use … explain …

A

a superconducting magnet - consists of many coils of wire through which an electric current is passed creating a magnetic field of up to 2.0 Tesla

42
Q

Maintaining such a large magnetic field consumes energy, explain how this is minimised …

A

minimised by reducing the resistance in the wire to almost zero by continually bathing them in liquid helium 269.1 below zero Celsius - insulated by a vacuum

43
Q

A strong magnetic field allows for … and superconductivity allows for …

A

high quality images, the system to operate economically

Physics - X-Ray I (7 decks)

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